This invention relates generally to the control of scrambling or encrypting of all or part of a duplex telecommunications circuit, and more particularly to the control of analog voice band scramblers over a total telecommunications circuit having tandem duplex links (or over as much of the total circuit as equipped). The system upon establishment of a communications link, will automatically configure the scramblers for a data exchange between end users.
Modern duplex telecommunications circuits (Circuits), whether voice or data, are often composed of multiple duplex telecommunications links (Links) connected in tandem. Some of these Links are particularly vulnerable to eavesdropping, compromising the privacy of the user. While end-to-end speech scrambling and data encrypting may be ultimate goals, a practical approach may generally start with the more vulnerable Links of a Circuit and grow gradually into an end-to-end secure Circuit. For example, a radiotelephone system is particularly vulnerable to eavesdropping. It would be advantageous, therefore, to scramble or encrypt the radio Link portion of a telephone Circuit first and add wireline protection later. This initial solution for the radio Link imposes the need for a companion scrambler/descrambler within the radiotelephone system's land infrastructure or at the system's telephone network interfacing. It is further desirable that when the far-end subscriber also becomes equipped with a companion terminal scrambler/descrambler, the entire Circuit be scrambled or encrypted.
Terminal scrambler/descramblers have been previously employed in several ways for scrambling the radio Link. The simplest adaptation requires both the radiotelephone subscriber station and the far-end subscriber station to be suitably equipped, and end-to-end protection is provided. This has been done with conventional analog voice band scramblers applied in a conventional way. It has also been done using digital scramblers. An example of this form of adaptation is provided by U.S. Pat. No. 4,815,128 assigned to the assignee of the present invention. Typically, the intermediate equipment placed at the interconnection point between the radio system and the telephone network receives an encoded signal from either the radio system or the telephone network and modifies and/or repeats the signal to the other.
In some applications, this additional processing of the encoded signal further corrupts the signal quality. One such application is that of limited bandwidth analog scrambling further described in U.S. Pat. No. 4,827,507 assigned to the assignee of the present invention.
Conventional terminal scramblers have also been adapted to radiotelephone service by inserting one in tandem in the Circuit that connects the radiotelephone system to the land network. This effectively secures the radio Link for those radiotelephone subscribers so equipped but offers no assistance in, and usually complicates, end-to-end scrambling.
Since the previous implementations envisioned either end-to-end or radio Link scrambling, but not both, there exists a need for a new and unique privacy scrambling system which will scramble the radio Link for radiotelephone subscribers equipped with terminal scramblers and yet provide end-to-end scrambling on calls in which the far-end subscriber is similarly equipped.